The market is basically in a holding pattern. New features tend to be situational and the performance improvements are pretty modest year-over-year. What's more, even old phones are fast enough for most uses, so even when the new one is 50% faster that's not a huge deal. It's hard to justify $800 to make a webpage load in .75 seconds instead of 1 second.
I'm still using my iPhone 6 and iOS 10 (I have some 32 bit apps that I still use). I'm considering swapping the battery instead of buying a new phone. Right now I would only upgrade if I severely broke it.
In some ways it would be a downgrade, because I use the headphone jack to wire it into my car's audio when doing navigation, and plug it into the cig lighter because navigation is a battery hog. It's pretty clear that Apple has no intention of ever bringing back the headphone jack.
Maybe I could find a bluetooth adapter on a headphone jack? I wonder if it could draw enough power from the headphone jack to not need a battery? Probably not.